The present invention relates to a water heater having immersed electrodes, in which the water is heated by resistance by the electric current flowing between the electrodes, this water heater comprising at least three electrodes connected in a delta configuration to a source of three-phase current and means for regulating the current.
It has already been proposed to produce a water heater of this type in German Pat. No. 356,288, the electrodes being mounted radially and symmetrically on an insulating support. The use of a three-phase current makes it possible to obtain a more favourable electric coefficient than with single-phase current consequently a greater efficiency.
In order that an installation of this type may be used practically, it is nevertheless necessary to be able to regulate the current consumed, not only depending on requirements, i.e. the desired temperature, but also depending on the admissible current intensity in a domestic supply system, taking into account the fact that this admissible intensity may also vary depending on other needs. Electrical regulating devices using circuit-breakers cut the supply current when the desired temperature of the water or ambient temperature is reached. However, this all or nothing operation is incompatible with domestic use under normal conditions, since sudden current variations, which are of the order of 25 amperes are not acceptable, taking into account the consumption of such an installation, in a domestic supply system without disturbing the latter.
Electronic regulating means such as thyratrons or triacs making it possible to keep the current at a constant value are currently available to the man skilled in the art. If the introduction of such a member into the supply circuit of the electrodes does not cause any problems in the case of a single-phase supply, this is not the case when there are three electrodes connected in a delta connection, as is the case of a water heater having immersed electrodes supplied with three-phase current, since if there is a thyratron or triac for each phase, the first of these members to open, allows a current equal to the sum of the currents in the two other members to pass, according to the law of feeding-points, which has the effect of putting the system out of equilibrium by modifying the angles of the currents in each of the phases. Furthermore, the resistivity of the water may vary greatly from one source to another, these variations completely modifying the working conditions and in particular the consumption of current and the heating time.